For example, a brake control system is described in Patent Document 1, in which braking force is controlled while a degree of freedom in controlling the fluid pressure in each of the wheel cylinders for four wheels is increased depending on a situation. This system includes both a power fluid pressure source in which pressure accumulation by an operating fluid is possible with the use of power and a manual fluid pressure source for increasing the pressure of the operating fluid in accordance with an amount of a brake operation by a driver, so that the fluid pressure in the wheel cylinder can be controlled by the respective fluid pressure sources. A fluid pressure channel, which commonly controls the left front wheel, right front wheel, left rear wheel, and right rear wheel, is connected to the power fluid pressure source to perform the control for increasing the pressure in each of the wheel cylinders for four wheels.
On the other hand, a fluid pressure channel for the front wheels, which controls the left front wheel and right front wheel, and that for the rear wheels, which controls the left rear wheel and right rear wheel, are connected to the manual fluid pressure source. Further, an isolation valve is provided, by which the channel for the left front wheel and right front wheel and that for the left rear wheel and right rear wheel can be isolated from each other. For example, when a pressure-increasing control from the power fluid pressure source cannot be sufficiently performed due to occurrence of fluid leakage in one of the aforementioned fluid pressure channels connected to the respective wheel cylinders, braking only by the fluid pressure channel for the front wheels or that for the rear wheels is performed: by switching to a fluid pressure control with the use of the manual fluid pressure source; and by isolating, from the manual fluid pressure source, the fluid pressure channel for the front wheels or that for the rear wheels, including the fluid pressure channel in which the fluid leakage has occurred, with the isolation valve being closed. Thus, by configuring a braking force control to be capable of being isolated into a control system for the front wheels and that for the rear wheels, braking force can be secured only by the front wheels or the rear wheels, thereby allowing a vehicle to be braked even if a failure occurs in one of the two fluid pressure channels.
Similarly, a brake control system having a power fluid pressure source and a manual fluid pressure source is disclosed in Patent Document 2. Also, in this system, a fluid pressure channel for front wheels and that for rear wheels are connected to the manual fluid pressure source such that a brake control can be performed only by the front wheels or rear wheels with the use of the manual fluid pressure source.